1. Field of the Invention
The invention relates to catalysts used in hydrodesulfurization and/or hydrodenitrogenation.
2. Discussion of the Background
The petroleum industry is increasingly utilizing coal, tar sands, heavy crudes and resids as sources for feedstocks. Feedstocks derived from these heavy materials contain greater quantities of sulfur and nitrogen than feedstocks derived from more conventional crude oils, and are consequently considered as being dirty feeds.
These feeds require extensive upgrading to obtain usable products therefrom. Such upgrading or refining is generally accomplished by hydrotreating processes which are well known in the petroleum industry and which include hydrodesulfurization and hydrodenitrogenation.
These processes require treating with hydrogen (H.sub.2) of various hydrocarbon fractions, or whole heavy feeds, or feedstocks, in the presence of hydrotreating catalysts to effect the removal of unwanted components, or compounds, or their conversion to innocuous or less undesirable compounds. In the treatment of catalytic cracking feedstocks, the cracking quality of the feedstock is improved by the hydrotreating. Carbon yield is reduced, and gasoline yield is generally increased.
Hydrotreating may be applied to many different feedstocks, e.g., solvents, light, middle or heavy distillate feeds and residual feeds, or fuel. In hydrotreating relatively light feeds, the feeds are treated with hydrogen, often to improve odor, color, stability, combustion characteristics, and the like. Unsaturated hydrocarbons are hydrogenated and saturated, while sulfur and nitrogen are removed.
In the hydrodesulfurization of heavier feedstocks, or residua, the sulfur compounds are hydrotreated and cracked. Carbon-sulfur bonds are broken, and most of the sulfur is converted to hydrogen sulfide (H.sub.2 S) which is removed as a gaseous species from the process.
Hydrodenitrogenation, to some extent occurs simultaneously with hydrodesulfurization reactions. In the hydrodenitrogenation of heavier feedstocks, or residua, the nitrogen compounds are hydrogenated and cracked. Carbon-nitrogen bonds are broken, and the nitrogen is removed from the process in the form of ammonia (NH.sub.3).
In the hydrosulfurization of relatively heavy feedstocks, emphasis is on the removal of sulfur from the feedstock. In the hydrodenitrogenation of relatively heavy feedstocks emphasis is on the removal of nitrogen from the feedstock.
Hydrotreating is thus one of the major processes in the oil industry. Today, the value of hydrotreating catalysts sold in the United States alone exceeds $50 million/year, and more than 20 million pounds of catalysts per year are consumed.
Hydrodesulfurization is used for petroleum or coal liquids feedstocks of every conceivable molecularweight range. The actual extent to which sulfur removal is effected will depend upon many factors, primarily the original sulfur content of the feedstock, the temperature at which treatment is effected, and the activity of the catalyst employed in the hydrodesulfurization reaction.
Typical hydrotreating catalysts are prepared by impregnation of support materials such as Al.sub.2 O.sub.3 with molybdenum or tungsten oxides which are promoted with cobalt or nickel. To achieve satisfactory activity, about 3.5% by weight of metallic cobalt and 15% molybdenum oxide are required. Most of the cobalt is rendered nearly inactive due to the formation of solid solutions with the Al.sub.2 O.sub.3 support.
Catalysts most commonly used for these hydrotreating reactions include materials such as cobalt molybdate on alumina, nickel on alumina, cobalt molybdate promoted with nickel, nickel tungstate, etc. Also, it is well known to those skilled in the art to use certain transition metal sulfides such as cobalt and molybdenum sulfides and mixtures thereof to upgrade oils containing sulfur and nitrogen compounds by catalytically removing such compounds in the presence of hydrogen, which processes are collectively known as hydrotreating or hydrorefining processes, it being understood that hydrorefining also includes some hydrogenation of aromatic and unsaturated aliphatic hydrocarbons.
Thus, U.S. Pat. No. 2,914,462 discloses the use of molybdenum sulfide for hydrodesulfurizing gas oil and U.S. Pat. No. 3,148,135 discloses the use of molybdenum sulfide for hydrorefining sulfur and nitrogen-containing hydrocarbon oils. U.S. Pat. No. 2,715,603, discloses the use of molybdenum sulfides for producing sulfur-free hydrogen and carbon dioxide, where the molybdenum sulfide converts carbonyl sulfide to hydrogen sulfide. Molybdenum and tungsten sulfides have other uses as catalysts, including hydrogenation, methanation, water gas shift, etc. reactions.
More recently, it has been disclosed in U.S. Pat. Nos. 4,243,553, and 4,243,554 that molybdenum sulfide catalysts of relatively high surface area may be obtained by thermally decomposing selected thiomolybdate salts at temperatures ranging from 300.degree. to 800.degree. C. in the presence of essentially inert, oxygenfree atmospheres. Suitable atmospheres are disclosed as consisting of argon, a vacuum, nitrogen and hydrogen.
In U.S. Pat. No. 4,243,554 an ammonium thiomolybdate salt is decomposed at a rate in excess of 15.degree. C. per minute, whereas in U.S. Pat. No. 4,243,553, a substituted ammonium thiomolybdate salt is thermally decomposed at a very slow heating rate of from about 0.5.degree. to 2.degree. C./min. The processes disclosed in these patents are claimed to produce molybdenum disulfide catalysts having superior properties for water gas shift and methanation reactions and for catalyzed hydrogenation or hydrotreating reactions.
U.S. Pat. No. 4,755,496, U.S. Pat. No. 4,698,145, U.S. Pat. No. 4,632,747, U.S. Pat. No. 4,666,878, U.S. Pat. No. 4,663,023, U.S. Pat. Nos. 4,650,563, and 4,705,619 disclose supported hydroprocessing catalysts prepared by heating a composite support material and one or more catalyst precursor salts under oxygen-free conditions and in the presence of sulfur at a temperature of at least about 200.degree. C. The precursor salt or salts are of the general formula (ML)(Mo.sub.y W.sub.1-y S.sub.4) or (ML)(Mo.sub.y W.sub.1-y O.sub.4) wherein M comprises one or more promoter metals which include Mn, Fe, Co, Ni, Zn and mixtures thereof, y is any value ranging from 0 to 1, and L is one or more neutral, nitrogencontaining ligands at least one of which is a chelating, polydentate ligand. All of these catalysts require using the neutral, nitrogen-containing ligand in their preparation. The absence of the neutral, nitrogen-containing ligand is reported to significantly lower the catalysts' hydrodesulfurization (HDS) activity. These catalysts are also prepared in the presence of water which makes their characterization impossible.
U.S. Pat. No. 4,581,125 discloses that hydrocarbon feeds can be upgraded by contacting them, at elevated temperature and in the presence of hydrogen, with a self-promoted catalyst formed by heating one or more carbon-containing, bis(tetrathiometallate) catalyst precursor salts selected from the group consisting of (NR.sub.4).sub.2 [M(WS.sub.4).sub.2), (NR.sub.4)[M(MoS.sub.4).sub.2 ] and mixtures thereof wherein R is one or more alkyl groups, aryl groups or mixtures thereof, wherein promoter metal M is covalently bound in the anion and is Ni, Co or Fe and wherein x is 2 if M is Ni and x is 3 if M is Co or Fe composite in a non-oxidizing atmosphere in the presence of sulfur, hydrogen, and a hydrocarbon to form the supported catalyst.
Engelhard has a catalyst, Sulfur Guard, that precedes reforming. The company maintains that because the catalyst operates in the gas phase, Sulfur Guard gets all the sulfur out. Competitive products, the company says, operate in the liquid phase (Oil & Gas Journal, June 24, 1987, 35).
Easy Active by Ketjen, a division of Akzo Chemie America, is a presulfided hydrotreating catalyst that spares refiners from sulfiding catalysts on the refinery site to achieve activation (Chemical Week, June 29, 1988, 54).
As of May, 1986, a Japanese catalyst manufacturer had demonstrated conversion of residual oil to lighter distillates, and low-sulfur and low-metal fuel oil. Idemitsu Kosan Co. Ltd. of Tokyo replaced a conventional resid catalyst with a new hydrodesulfurization catalyst (R-HYC 4) in a modified commercial hydrodesulfurization unit, producing 85-90% desulfurization. Benefits of the catalyst include: (1) High activity to crack heavy residues selectively to desired smaller hydrocarbons; (2) High hydrogenation activity in optimum combination with cracking activity; (3) High tolerance to contaminants in feedstocks such as metals and coke precursors; (4) High demetallization and deasphalting activity (Oil & Gas Journal, May 26, 1986, 51-52).
However there remains a strongly felt need for hydrodesulfurization/hydrodenitrogenation catalysts which are imbued with high activity, which are stable and which can be designed to control the product(s) produced from the catalytic process.